Electric pump

ABSTRACT

A driving timing gear is located between an electric motor and a driving rotor with respect to an axial direction of a driving shaft. A first bearing is located on the same side of the driving rotor as the driving timing gear. The driving shaft has a rotor attaching end. The rotor attaching end is a free end that is located on the same side of the first bearing as the driving rotor. A weight is at a portion of the driving rotor that is close to the driving timing gear with respect to the axial direction of the driving shaft. Another weight is located at a portion of a driven rotor that is closer to a driven timing gear.

BACKGROUND OF THE INVENTION

The present invention relates to an electric pump in which a bearing is located between a driving rotor and a driving timing gear, and a free end of a driving shaft is located on a side opposite to the driving timing gear with respect to the driving rotor.

As shown in FIG. 5, a Roots pump 90 disclosed in Japanese Laid-Open Patent Publication No. 2006-214380 includes a driving shaft 91 and a driven shaft 96. The driving shaft 91 has a rotor attaching end 91 a to which a driving rotor 93 is attached. The driven shaft 96 has a rotor attaching end 96 a to which a driven rotor 97 is attached. When rotation of an electric motor M is transmitted to the driven timing gear 92 b through a driving timing gear 92 a, the driven shaft 96 rotates in synchronization with the driving shaft 91. As a result, the Roots pump 90 draws and discharges fluid. The driving timing gear 92 a is located between the electric motor M and the driving rotor 93.

The Roots pump 90 has three bearings, or a first bearing 94, a second bearing 95, and a third bearing 98. The first bearing 94 rotatably supports the driving shaft 91 between the driving timing gear 92 a and the driving rotor 93. The second bearing 95 rotatably supports the driven shaft 96 between the driven timing gear 92 b and the driven rotor 97. The driving shaft 91 can be considered as a cantilever that is supported by the first bearing 94 in a cantilever manner, and the rotor attaching end 91 a of the driving shaft 91 is a free end. The driven shaft 96 can be considered as a cantilever that is supported by the second bearing 95 in a cantilever manner, and the rotor attaching end 96 a of the driven shaft 96 is a free end. The third bearing 98 rotatably supports a motor attaching end 91 b of the driving shaft 91.

The center of gravity G1 of the driving rotor 93 is located at the center of the driving rotor 93 in the axial direction, that is, at a center of thickness of the driving rotor 93. The center of gravity G2 of the driven rotor 97 is located at the center of the driven rotor 97 in the axial direction, that is, at a center of thickness of the driven rotor 97.

The weight of the driving rotor 93 can bend the driving shaft 91 in relation to the first bearing 94, and the weight of the driven rotor 97 can bend the driven shaft 96 in relation to the second bearing 95. During the operation of the Roots pump 90, the driving shaft 91 and the driven shaft 96 undergo precession due to the clearance within the first bearing 94 and the clearance within the second bearing 95, which can produce vibration and noise. For example, the driving rotor 93 and the driven rotor 97 contact each other and produce noise.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide an electric pump that reduces vibration of rotary shafts.

In accordance with one aspect of the present invention, an electric pump that includes an electric motor and a first rotary shaft driven by the electric motor is provided. The electric pump includes a first rotor fixed to the first rotary shaft, a first timing gear provided to the first rotary shaft, and a first bearing supporting the first rotary shaft. The first bearing is located on the same side of the first rotor as the first timing gear. The first rotary shaft has a free end that is located on the same side of the first bearing as the first rotor. A first weight is provided to the first rotor so as to rotate integrally with the first rotor. The material of the first weight has a specific gravity greater than that of the material of the first rotor. The first weight is located at a position of the first rotor that is close to the first timing gear with respect to the axial direction of the first rotary shaft. The electric pump includes a second rotary shaft, a second rotor fixed to the second rotary shaft, and a second timing gear provided to the second rotary shaft. The first timing gear and the second timing gear cause the second rotary shaft to rotate synchronously with the first rotary shaft. The first timing gear is located between the electric motor and the first rotor with respect to the axial direction of the first rotary shaft. The second timing gear is located between the electric motor and the second rotor with respect to the axial direction of the second rotary shaft. A second bearing supports the second rotary shaft. The second bearing is located on the same side of the second rotor as the second timing gear. The second rotary shaft has a free end that is located on the same side of the second bearing as the second rotor. A second weight is provided to the second rotor so as to rotate integrally with the second rotor. The material of the second weight has a specific gravity greater than that of the material of the second rotor. The second weight is located at a position of the second rotor that is close to the second timing gear with respect to the axial direction of the second rotary shaft.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a cross-sectional view illustrating an electric Roots pump according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 1;

FIGS. 4A and 4B are partial cross-sectional views each illustrating an electric Roots pump according to a modified embodiment; and

FIG. 5 is a cross-sectional view illustrating a prior art Roots pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 to 3 show one embodiment of the present invention. FIG. 1 shows an electric pump according to the present embodiment, which is a Roots pump 10. Arrow Y of FIG. 1 represents a direction from the rear toward the front of the Roots pump 10.

As shown in FIG. 1, a pump housing 10 a, which is the housing of the Roots pump 10, includes a rotor housing member 11, a bearing housing member 12, a gear housing member 13, and a motor housing member 14 arranged in this order from the rear toward the front. The bearing housing member 12 is secured to the front end of the rotor housing member 11, the gear housing member 13 is secured to the front end of the bearing housing member 12, and the motor housing member 14 is secured to the front end of the gear housing member 13.

The rotor housing member 11 defines a pump chamber 15 that accommodates a first rotor, which is a driving rotor 22, and a second rotor, which is a driven rotor 23, and the bearing housing member 12 covers the opening of the pump chamber 15. The gear housing member 13 defines a gear chamber 16 that accommodates a first timing gear, which is a driving timing gear 28, and a second timing gear, which is a driven timing gear 29. The bearing housing member 12 lids the gear chamber 16. The motor housing member 14 defines a motor chamber 17 that accommodates an electric motor M. The gear housing member 13 lids the motor chamber 17.

The pump housing 10 a accommodates a first rotary shaft, which is a driving shaft 20, and a second rotary shaft, which is a driven shaft 21. The driving shaft 20 and the driven shaft 21 extend parallel to each other in a direction along arrow Y.

The Roots pump 10 has four bearings, that is, a first bearing 31, a second bearing 32, a third bearing 33, and a fourth bearing 34. The first bearing 31 and the third bearing 33 rotatably support the driving shaft 20, and the second bearing 32 and the fourth bearing 34 rotatably support the driven shaft 21. The bearing housing member 12 has the first bearing 31 and the second bearing 32, the motor housing member 14 has the third bearing 33, and the gear housing member 13 has the fourth bearing 34.

The driving shaft 20 extends from the rear toward the front through the driving rotor 22, a shaft sealing member 35 a, the first bearing 31, the driving timing gear 28, a shaft sealing member 35 b, the electric motor M, and the third bearing 33 in this order. The driving rotor 22, the driving timing gear 28, and the rotor of the electric motor M rotate integrally with the driving shaft 20.

The driven shaft 21 extends from the rear toward the front through the driven rotor 23, a shaft sealing member 35 c, the second bearing 32, the driven timing gear 29, and the fourth bearing 34 in this order. The driven rotor 23 and the driven timing gear 29 rotate integrally with the driven shaft 21.

As shown in FIGS. 2 and 3, the driving rotor 22 and the driven rotor 23 are each a two-lobe type Roots rotor. A cross section of each of the rotors 22, 23 perpendicular to the axial direction is shaped like a gourd. The driving rotor 22 has a pair of driving lobes 24 extending radially outward from the driving shaft 20 in opposite directions. Also, two driving recesses 25 are formed between the driving lobes 24. Likewise, the driven rotor 23 has a pair of driven lobes 26 extending radially outward from the driven shaft 21 in opposite directions. Also, two driven recesses 27 are formed between the driven lobes 26. That is, a pair of the driving lobes 24 are arranged in the circumferential direction at an equal interval, and the driven lobes 26 are also arranged in circumferential direction at an equal interval.

The outer surface of the driving rotor 22, the outer surface of the driven rotor 23, and the inner surface of the rotor housing member 11 define the pump chamber 15. As shown in FIG. 3, the rotor housing member 11 has a suction port 18 for drawing fluid into the pump chamber 15, and a discharge port 19 for discharging fluid from the pump chamber 15.

The driving timing gear 28 and the driven timing gear 29 form pair of timing gears meshed with each other. When the electric motor M rotates the driving shaft 20, the rotation of the driving shaft 20 is transmitted from the driving timing gear 28 to the driven timing gear 29, so that the driven shaft 21 rotates synchronously with the driving shaft 20. As a result, the driving rotor 22 and the driven rotor 23 rotate in opposite directions, so that fluid is drawn into the pump chamber 15 through the suction port 18, and is discharged to the outside through the discharge port 19.

The relative positions of the components will now be described.

The rear end of the driving shaft 20 is referred to as a rotor attaching end 20 a, to which the driving rotor 22 is attached. The front end of the driving shaft 20 is rotatably supported by the third bearing 33. The rear end of the driven shaft 21 is referred to as a rotor attaching end 21 a, to which the driven rotor 23 is attached. The front end of the driven shaft 21 is rotatably supported by the fourth bearing 34.

The driving timing gear 28 is located between the electric motor M and the driving rotor 22 with respect to the axial direction of the driving shaft 20. The driven timing gear 29 is located between the electric motor M and the driven rotor 23 with respect to the axial direction of the driven shaft 21. The first bearing 31 is located between the driving rotor 22 and the driving timing gear 28, and the second bearing 32 is located between the driven rotor 23 and the driven timing gear 29. That is, the driving shaft 20 can be considered as a cantilever that is supported by the first bearing 31 in a cantilever manner, and the rotor attaching end 20 a is a free end of the driving shaft 20. Likewise, the driven shaft 21 can be considered as a cantilever that is supported by the second bearing 32 in a cantilever manner, and the rotor attaching end 21 a is a free end of the driven shaft 21. The weight of the driving rotor 22 can be considered as load acting on the driving shaft 20, which is a cantilever. Similarly, the weight of the driven rotor 23 can be considered as load acting on the driven shaft 21, which is a cantilever.

In other words, the first bearing 31 supports the driving shaft 20 at a side corresponding to the driving timing gear 28 with respect to the driving rotor 22, thus the driving shaft 20 is supported by the first bearing 31 in a cantilever manner. Further, the second bearing 32 supports the driven shaft 21 at a side corresponding to the driven timing gear 29 with respect to the driven rotor 23, thus the driven shaft 21 is supported by the second bearing 32 in a cantilever manner.

The driving rotor 22 has a bearing facing surface 22 a that faces the first bearing 31 and a free end surface 22 b opposite to the bearing facing surface 22 a. The free end surface 22 b is located on the same plane as the end face of the rotor attaching end 20 a and faces the rear wall of the rotor housing 11. Likewise, the driven rotor 23 has a bearing facing surface 23 a that faces the second bearing 32 and a free end surface 23 b opposite to the bearing facing surface 23 a. The free end surface 23 b is located on the same plane as the end face of the rotor attaching end 21 a and faces the rear wall of the rotor housing 11.

The driving rotor 22 and the driven rotor 23 will now be described.

As shown in FIGS. 1 to 3, the driving rotor 22 has a pair of first through holes, which are through holes 50 each axially extending through one of the driving lobes 24. A pair of the through holes 50, which are each formed as a circular hole, are located at opposite positions to each other with respect to the driving shaft 20. Each through hole 50 is located in a radial center of the corresponding driving lobe 24. The center of gravity G1 of the driving rotor 22 is located at the center of the driving rotor 22 in the axial direction.

A disc-shaped first weight, which is a weight 60, is press fitted into each through hole 50. As shown in FIGS. 1 and 2, each weight 60 is located between the center of gravity G1 of the driving rotor 22 and a bearing facing surface 22 a. In other words, each weight 60 is located on a side of the center of gravity G1 of the driving rotor 22 that corresponds to the first bearing 31, that is, on a side that corresponds to the driving timing gear 28. That is, the weight 60, which serves as a first weight, is located in a portion of the driving rotor 22 that is close to the driving timing gear 28 with respect to the axial direction. As a result, the center of gravity J1 of the combined unit of the driving rotor 22 and the weight 60 is shifted toward the first bearing 31 from the center of gravity G1 of the single driving rotor 22. As shown in FIGS. 1 and 3, the part of the through hole 50 that is rearward of the weight 60, for example, remains hollow.

To reliably suppress vibration of the driving shaft 20, the axial measurement and the mass of the weight 60 are adjusted to adjust the position of the center of gravity J1.

Likewise, the driven rotor 23 has a pair of second through holes, which are through holes 51 each axially extending through one of the driven lobes 26. A pair of the through holes 51, which are each formed as a circular hole, are located at opposite positions to each other with respect to the driven shaft 21. Each through hole 51 is located in a radial center of the corresponding driven lobe 26. The center of gravity G2 of the driven rotor 23 is located at the center of the single driven rotor 23 in the axial direction.

A disc-shaped second weight, which is a weight 60, is press fitted into each through hole 51. Each weight 60 is located between the center of gravity G2 of the driven rotor 23 and a bearing facing surface 23 a. In other words, each weight 60 is located on a side of the center of gravity G2 of the driven rotor 23 that corresponds to the second bearing 32, that is, on a side that corresponds to the driven timing gear 29. That is, the weight 60, which serves as a second weight, is located in a portion of the driven rotor 23 that is close to the driven timing gear 29 with respect to the axial direction. As a result, the center of gravity J2 of the combined unit of the driven rotor 23 and the weight 60 is shifted toward the second bearing 32 from the center of gravity G2 of the single driven rotor 23.

To reliably suppress vibration of the driven shaft 21, the axial measurement and the mass of the weight 60 are adjusted to adjust the position of the center of gravity J2.

For example, the weight 60 is made of an iron based material, and the driving rotor 22 and the driven rotor 23 are made of an aluminum based material such that the specific gravity of the weight 60 is greater than those of the driving rotor 22 and the driven rotor 23.

The preferred embodiment has the following advantages.

(1) The weights 60 are attached to portions of the driving rotor 22 that are close to the driving timing gear 28. Therefore, the center of gravity J1 of the combined unit of the driving rotor 22 and the weight 60 is shifted toward the first bearing 31 from the center of gravity G1 of the single driving rotor 22. As a result, precession of the driving rotor 22 is suppressed, and vibration and noise of the driving rotor 22 are suppressed accordingly. Particularly, vibration and noise during high speed operation of the driving rotor 22 are suppressed.

Likewise, the weights 60 are attached to portions of the driven rotor 23 that are close to the driven timing gear 29. Therefore, the center of gravity J2 of the combined unit of the driven rotor 23 and the weight 60 is shifted toward the second bearing 32 from the center of gravity G2 of the single driven rotor 23. As a result, precession of the driven rotor 23 is suppressed, and vibration and noise of the driven rotor 23 are suppressed accordingly. Particularly, vibration and noise during high speed operation of the driven rotor 23 are suppressed.

(2) Since vibration of the driving shaft 20 and the driven shaft 21 are suppressed, the power loss of the electric motor M is reduced. Thus, the performance of the Roots pump 10 at high speeds is improved, and the size and the weigh of the electric motor M and the Roots pump 10 can be reduced.

(3) The driving rotor 22 and the driven rotor 23 each have the through holes 50, 51 for accommodating the weights 60. That is, portions of the driving rotor 22 and the driven rotor 23 are removed so that the weights are reduced. This allows the size of the electric motor M to be reduced. The size and the weight of the Roots pump 10 are therefore further reduced.

(4) The weights 60, which are symmetrical with respect to the driving shaft 20, are provided in a pair of the driving lobes 24, and the weights 60, which are symmetrical with respect to the driven shaft 21, are provided in a pair of the driven lobes 26. This, for example, prevents the weights 60 from decentering the driving rotor 22 and the driven rotor 23. Thus, accurate synchronizing timing of the driving rotor 22 and the driven rotor 23 is easily maintained.

(5) The rotor attaching end 20 a of the driving shaft 20 and the rotor attaching end 21 a of the driven shaft 21 are free ends. Thus, the Roots pump 10 has a reduced number of bearings for rotatably supporting the driving shaft 20 and the driven shaft 21. Accordingly, the number of shaft sealing members for sealing the driving shaft 20 and the driven shaft 21 is reduced. Therefore, the power loss due to shaft sealing members is reduced.

(6) The greater the distance between the center of gravity G1 of the driving rotor 22 and the first bearing 31, and the greater the distance between the center of gravity G2 of the driven rotor 23 from the second bearing 32, the more intense the precession of the driving shaft 20 and the driven shaft 21 is likely to become. In the present embodiment, the weights 60 cause the centers of gravity J1, J2 to be shifted toward the first bearing 31 and the second bearing 32 with respect to the centers of gravity G1, G2. The present embodiment is therefore suitable for a Roots pump 10 having elongated driving rotor 22 and driven rotor 23.

(7) Vibration and noise of the driving shaft 20 are suppressed by simply forming the through holes 50 in the driving rotor 22, and press fitting the weights 60 in the through holes 50. Also, vibration and noise of the driven shaft 21 are suppressed by simply forming the through holes 51 in the driven rotor 23, and press fitting the weights 60 in the through holes 51. Further, vibration and noise of the driving shaft 20 and the driven shaft 21 are suppressed by a simple operation by adjusting the mass of the weights 60.

The above-mentioned embodiment may be modified as follows.

As shown in FIG. 4A, a plate-like weight 61 may be bonded to the bearing facing surface 22 a of the driving rotor 22, and likewise, another thin plate-like weight 61 may be bonded to the bearing facing surface 23 a of the driven rotor 23. These weights 61 may be each sized to expand over the entirety of the corresponding one of the bearing facing surfaces 22 a, 23 a. In this case, compared to the case in which the weights 60 are press fitted into the through hole 50, 51, the mass of each weight 61 is adjusted more freely. Also, since the through holes 50, 51 can be omitted from the driving rotor 22 and the driven rotor 23, the driving rotor 22 and the driven rotor 23 do not need to be subject to post-machining for forming the through holes 50, 51. The production efficiency of the driving rotor 22 and the driven rotor 23 is thus easily improved.

The configuration shown in FIG. 4B may be employed. In this configuration, the through holes 50 are omitted, and attachment recesses 52 are formed on the bearing facing surface 22 a of the driving rotor 22. Disc-shaped weights 62 are press fitted into or adhered to the attachment recesses 52. Likewise, the through holes 51 may be omitted, and attachment recesses 52 may be formed on the bearing facing surface 23 a of the driven rotor 23, and disc-shaped weights 62 may be press fitted into or adhered to the attachment recesses 52. The attachment recesses 52 are formed simultaneously with the driving rotor 22 and the driven rotor 23 when molding the rotors 22, 23. As in the above described modification, the driving rotor 22 and the driven rotor 23 do not need to be subject to post-machining for forming the through holes 50, 51. The production efficiency of the driving rotor 22 and the driven rotor 23 is thus easily improved.

The driving rotor 22 and the driven rotor 23 may be formed of resin. In this case, the weights 60 are made of a metal material having a specific gravity greater than that of the resin. For example, the weights 60 are made of an iron-based material.

The weights 60 may be embedded in the driving rotor 22 and the driven rotor 23 through casting.

As long as the driving rotor 22 and the driven rotor 23 are Roots rotors each having two or more lobes, the rotors 22, 23 may each have three lobes. When the driving rotor 22 and the driven rotor 23 each have an odd number of lobes, weights 60 are preferably provided in all of the driving lobes 24 and the driven lobes 26.

The driving shaft 20 may have a plurality of driving rotors 22, and the driven shaft 21 may have a plurality of driven rotors 23. That is, the present invention is not limited to a single-stage Roots pump section, but may be embodied in a multi-stage Roots pump.

The driving rotor 22 and the driven rotor 23 do not need to be Roots rotors, but may be screw rotors. That is, the electric pump may be an electric screw pump. 

1. An electric pump, comprising: an electric motor; a first rotary shaft driven by the electric motor; a first rotor fixed to the first rotary shaft; a first timing gear provided to the first rotary shaft, the first timing gear being located between the electric motor and the first rotor with respect to the axial direction of the first rotary shaft; a first bearing supporting the first rotary shaft, the first bearing being located on the same side of the first rotor as the first timing gear, wherein the first rotary shaft has a free end that is located on the same side of the first bearing as the first rotor; a first weight provided to the first rotor so as to rotate integrally with the first rotor, wherein the material of the first weight has a specific gravity greater than that of the material of the first rotor, and the first weight is located at a portion of the first rotor that is close to the first timing gear with respect to an axial direction of the first rotary shaft; a second rotary shaft; a second rotor fixed to the second rotary shaft; a second timing gear provided to the second rotary shaft, the first timing gear and the second timing gear causing the second rotary shaft to rotate synchronously with the first rotary shaft, and the second timing gear being located between the electric motor and the second rotor with respect to an axial direction of the second rotary shaft; a second bearing supporting the second rotary shaft, the second bearing being located on the same side of the second rotor as the second timing gear, wherein the second rotary shaft has a free end that is located on the same side of the second bearing as the second rotor; and a second weight provided to the second rotor so as to rotate integrally with the second rotor, wherein the material of the second weight has a specific gravity greater than that of the material of the second rotor, and the second weight is located at a portion of the second rotor that is close to the second timing gear with respect to the axial direction of the second rotary shaft.
 2. The electric pump according to claim 1, wherein the first rotor and the second rotor are Roots type, each of the first rotor and the second rotor having a plurality of lobes arranged at equal angular intervals along a circumferential direction of the first rotary shaft and along a circumferential direction of the second rotary shaft, respectively, and a plurality of recesses each located between an adjacent pair of the lobes, wherein the first rotor has a first through hole extending along the axial direction, the first weight being arranged in the first through hole, and wherein the second rotor has a second through hole extending along the axial direction, the second weight being arranged in the second through hole.
 3. The electric pump according to claim 2, wherein the first rotor and the second rotor are each a two-lobe type, wherein the two lobes of the first rotor are located on opposite sides of the first rotary shaft, each lobe having the first through hole, and wherein the two lobes of the second rotor are located on opposite sides of the second rotary shaft, each lobe having the second through hole.
 4. The electric pump according to claim 1, wherein the first weight is located on an end face of the first rotor that faces the first timing gear, and wherein the second weight is located on an end face of the second rotor that faces the second timing gear. 